The Volkswagen Quantum front side marker uses a P21/5W bulb size while the rear side marker requires a 12821 bulb size. The replacement chart covers 1987 to 1988 vehicle production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Volkswagen Quantum uses two distinct bulb types across its front and rear side marker positions for the 1987-1988 model years.
The P21/5W is a dual-filament bulb built to ECE standards, meaning it meets European and international regulatory requirements. It operates at 12V and carries two wattage ratings, 21W and 5W, each corresponding to a separate filament within the same housing.
The P21/5W uses a BAY15d bayonet base, an offset two-pin fitting designed to prevent incorrect installation by ensuring the bulb can only be seated in one orientation.
The Volkswagen Quantum uses the P21/5W in the front side marker position for both the 1987 and 1988 model years.
The 12821 is a Philips part number designation for a miniature wedge bulb of the T10 type. It operates at 12V with a single 5W output and uses a W2.1x9.5d wedge base, which requires no locking mechanism as the base itself creates a friction fit within the socket.
The rear side marker position on the Volkswagen Quantum calls for the 12821 bulb across both the 1987 and 1988 model years.
The front and rear side marker positions on the Quantum are not interchangeable in terms of bulb fitment. The front uses a dual-filament bayonet bulb while the rear uses a single-filament wedge bulb, and the two base types are physically incompatible with each other's sockets.
The P21/5W and 12821 differ not only in base type but also in filament count and maximum wattage, making substitution between the two positions technically incorrect regardless of voltage compatibility.